The use of bitumen in the manufacture of materials for highway and industrial applications has long been known: bitumen is the main hydrocarbon binder used in the field of highway construction or civil engineering. For use as a binder in these various applications, bitumen must have some particular physicochemical properties. One of the most important properties is the consistency of the bitumen; this must be high enough at the temperatures of use to avoid the formation of ruts caused by traffic.
The bitumen must also be elastic to resist the deformations imposed by traffic and/or changes in temperature, phenomena which lead to cracking of the bituminous mixes or to stripping of the surface aggregates. Finally, the bitumen must be sufficiently fluid at the lowest possible temperatures of application to allow good coating of the aggregates and the placement of the bituminous mix on the road as well as compacting thereof with the current technical means of the highway profession. The implementation of a bituminous binder therefore requires combining both the hardness and the elasticity of bitumen at the temperatures of use and low viscosity at the temperatures of application. As bitumen on its own is not generally sufficiently elastic, polymers, which may optionally be cross-linked, are added to the bitumen. These cross-linked polymers give the bituminous compositions greatly improved elastic properties and stability in storage.
However, when hot, addition of polymers to the bituminous composition leads as a general rule to an increase in viscosity of the bituminous composition. To be suitable for application on the carriageway, the bituminous binder with added polymers will therefore have to be heated to an application temperature higher than that of a bituminous binder without polymers. This runs counter to the objectives of saving energy, lowering the temperatures of use, reducing emissions of fumes on the construction site and worker protection.
Cross-linking according to the prior art is in most cases irreversible cross-linking based on the formation of covalent bonds between the polymers. Thus, one of the forms of cross-linking most used in the field of bitumens is cross-linking with sulphur or vulcanization. The applicant has developed and patented a certain number of cross-linked bituminous compositions having properties that are greatly improved relative to bitumen without polymers and relative to the non-cross-linked bitumen/polymer physical mixture. Among the applicant's patents, there may be mentioned in particular the following references: FR2376188, FR2429241, EP0799280, EP0690892.
Recently, in two patent applications WO2008107551 and WO2009101275, the applicant described a new method of reversible cross-linking of bituminous compositions, based on the use of organogelling additives. The applicant in particular showed that the organogelling additive may be assimilated to a “supramolecular” polymer and imparts to bitumen with properties equivalent to those of a conventional bitumen/polymer composition, in particular with respect to hardness, while reducing the high-temperature viscosity. The thermoreversibly cross-linked bituminous compositions thus obtained are hard at the temperatures of use and have reduced viscosity at the application temperatures.
Continuing this work, the applicant looked for other compounds allowing bitumens to be hardened at the temperatures of use without increasing their high-temperature viscosity. A further objective of the applicant is to propose new additives capable of improving the rheological properties of a bituminous composition or of a bitumen base, in particular for adjusting the mechanical characteristics of said composition or bitumen base depending on the applications for which the composition is intended.
The mechanical properties of bituminous compositions are generally assessed by determining a series of mechanical characteristics using standardized tests, those used most widely being the softening point determined by the ring and ball test, also called the ring and ball softening point and denoted by RBT, and needle penetration expressed in 1/10 of mm. An indication of the susceptibility to temperature of bituminous compositions can also be obtained from a correlation between the needle penetration and the RBT of said compositions, known as the penetration index or Pfeiffer index, denoted by PI. The susceptibility to temperature of the bituminous composition decreases as the PI value increases. Low susceptibility to temperature ensures good mechanical behaviour over the temperature range of use of said composition. The applicant therefore concentrated on the effect of additives on the penetration index (or Pfeiffer index, denoted PI), ring and ball softening point (RBT), needle penetration and/or the dynamic viscosity of the bituminous compositions, at a temperature above or equal to 80° C., preferably above 80° C., more preferably above or equal to 120° C.
The invention aims in particular to thermoreversibly cross-linked bituminous compositions, i.e. having, at the temperatures of use, the properties of conventional bituminous compositions with respect to hardness and having reduced viscosity at the application temperatures. Another object of the invention is to propose a simple method for preparing thermoreversibly cross-linked bituminous compositions. According to the invention, this object is achieved with bituminous compositions having improved thermoreversible and rheological properties, in particular having low dynamic viscosity at a temperature above or equal to 80° C., preferably above 80° C., more preferably above or equal to 120° C., without impairing the consistency of said compositions at the temperatures of use.
In particular, the bituminous composition according to the invention comprises:
a bitumen,
a first additive comprising at least one fatty acid ester function, saturated or unsaturated, having a hydrocarbon chain with 4 to 36 carbon atoms, linear or branched, optionally substituted by at least one hydroxyl group,
a second additive comprising at least one organogelator of the following general formula (I) or (II):R1—CONH—X—NHCO—R2  (I)in which the groups R1, R2 and X are identical or different and represent independently a hydrocarbon chain with 4 to 36 carbon atoms, saturated or unsaturated, linear or branched, cyclic or acyclic and comprising, optionally, at least one heteroatom selected from O, N and S, preferably O.R3—(COOH)z  (II)in which R3 is a linear or branched, saturated or unsaturated hydrocarbon chain with 4 to 68 carbon atoms and z is an integer in the range from 2 to 4. According to a particular development, the bituminous composition is cross-linked thermoreversibly.
According to another particular embodiment, the first additive has a general formula (III) as follows:
in which
G1 represents a saturated or unsaturated, linear or branched aliphatic hydrocarbon chain with 4 to 36 carbon atoms, optionally substituted by at least one hydroxyl group,
G2 represents a saturated or unsaturated, linear or branched aliphatic hydrocarbon chain with 1 to 188 carbon atoms, optionally comprising at least one ester function and/or at least one hydroxyl group.
Preferably, G2 comprises at least one ester function. According to a preferred variant, G2 comprises at least one ester function and at least one hydroxyl group.
According to a preferred variant, the first additive is selected from the group consisting in the saturated or unsaturated mono-, di-, tri-, tetra-, penta- and hexa-esters of fatty acid, comprising at least one linear or branched hydrocarbon chain with 4 to 36 carbon atoms, optionally substituted by at least one hydroxyl group. Preferably, the first additive is selected from the group consisting in the mono-, di- and tri-glycerides of fatty acids, the mono-, di- and tri-glycerides of hydroxy fatty acids, the fatty acid mono-, di-, tri- and tetra-esters of pentaerythritol (PET) and the fatty acid mono-, di-, tri-, tetra-, penta- and hexa-esters of dipentaerythritol (diPET). Advantageously, the first additive is selected from the triglycerides of fatty acids comprising three hydrocarbon chains, identical or different, each independently having from 4 to 36 carbon atoms, saturated or unsaturated, linear or branched, optionally substituted by at least one hydroxyl group. Whatever the type of fatty acid ester of the first additive, saturated fatty acid derivatives will be preferred.
According to another preferred particular embodiment, the organogelator represented by formula (II) is a diacid of general formula HOOC—(CH2)w—COOH with w an integer in the range from 4 to 22, preferably from 4 to 18. The organogelator represented by formula (II) is preferably a diacid selected from the group consisting in adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, 1,2-dodecanedioic acid and tetradecanedioic acid.
According to another preferred particular embodiment, the organogelator is represented by formula (I) in which X represents the group —(CH2)p— with p being comprised between 1 and 8, preferably between 1 and 4. According to a variant, the organogelator is represented by formula (I) in which R1 and R2 are identical or different and represent, independently, a saturated, acyclic, linear or branched hydrocarbon chain with 4 to 36 carbon atoms, and optionally at least one heteroatom. The organogelator is preferably N,N′-ethylene-bis(stearamide). Preferably, the bituminous composition comprises from 0.1 to 10% by weight of the first and second additives relative to the weight of bitumen.
The combined presence of the first and second additives surprisingly imparts to bitumen bases or bituminous compositions, with improved mechanical and rheological properties, in particular an unexpected lowering of the dynamic viscosity at a temperature above or equal to 80° C., preferably above 80° C., while preserving good consistency at the temperatures of use. In these earlier works (WO2008107551 and WO2009101275), the applicant showed that adding an organogelator made it possible to harden the bituminous composition without increasing the high-temperature viscosity of the bituminous composition.
The applicant has now been able to demonstrate that the combination of a first specific additive and a second specific additive comprising a particular organogelator has a quite unexpected remarkable effect on the susceptibility to temperature of the bituminous composition, in particular on the viscosity at the temperature of application and, advantageously, on the PI index at the temperature of use while maintaining the hardening effect of the organogelator mentioned in the patent applications of the prior art (WO2008107551). The bituminous compositions according to the invention rectify the drawbacks of the prior art and satisfy the objectives of the invention. It will be demonstrated later on in the description that such a combination of additives makes it possible to lower the dynamic viscosity at a temperature above or equal to 80° C., preferably above 80° C., not only relative to the initial bitumen base but also, quite surprisingly, relative to a bituminous composition comprising either the first additive or the second additive of the organogelator type.
The invention further relates to the use of such a bituminous composition according to the invention, to manufacture a bituminous binder and said bituminous binder in particular in the form of a synthetic binder, an anhydrous binder, a bituminous emulsion, a polymeric bitumen or a fluxed bitumen. The invention also relates to a method of preparing such a bituminous composition according to the invention, in which the first and second additives are added, at temperatures in the range from 100 to 180° C., preferably in the range from 120° C. to 140° C., either to the bitumen alone, to the bitumen whether or not modified by polymers, to the bitumen in the form of bituminous binder or to the bitumen when the latter is in the form of anhydrous binder, bituminous mix, or surface dressing, or during manufacture of said bitumen, bituminous mixes, binders or coatings. According to the invention, this object is also achieved by a bituminous mix comprising such a composition according to the invention, aggregates of bituminous mixes and mineral and/or synthetic fillers.
The invention also relates to the use of a combination of a first additive and a second additive in a bituminous composition or a bitumen base, for thermoreversibly cross-linking said bituminous composition or bitumen base. The use makes it possible, in particular, to lower the dynamic viscosity of a bituminous composition or of a bitumen base at a temperature above or equal to 80° C., preferably above 80° C., without impairing the consistency of said composition at the temperatures of use.
In particular, the invention relates to such a use for increasing the softening point determined by the ring and ball test according to standard EN 1427 (RBT) and the penetration index (or Pfeiffer index, PI) while lowering the dynamic viscosity at a temperature above or equal to 80° C., preferably above 80° C., of said composition or bitumen base. According to a preferred variant, the use of such a combination is particularly effective for lowering the needle penetration at 25° C. according to standard EN 1426 (P25) of said composition or bitumen base. According to a development of the invention, when the first additive comprises an organogelator of general formula (I), the use of such a combination makes it possible to increase the softening point determined by the ring and ball test according to European standard EN 1427 (RBT) and the penetration index (or Pfeiffer index, PI), and to lower the dynamic viscosity of the bituminous composition or bitumen base, at a temperature above or equal to 80° C., preferably above 80° C.